A CABLE LEAD-IN

Abstract: A cable lead-in (1) comprises an upper part (2) and a lower part (3). The upper part and the lower part (2, 3) are clamped together by means of a threaded joint in an opening (7) in a wall (6) on a casing around current conductors (non shown), which are connected via an electric cable (11) to other current conductors (not shown) outside the casing. The upper part (2) is formed with a through duct (10), which has an outer funnel-shaped duct section (12) and an inner threaded section (13). A seat (14) for a sealing ring (15) is formed between these two sections. A nipple (16) having a strain relief strap (20) is screwed into the threaded section (13), whereby the sealing ring (15) is pressed sealingly against both the seat (14) and the cable (11). The funnel-shaped duct section (12) serves to protect the cable (11) against damage by bending in operation. The nipple (16) has a hexagonal head (18), and at least one of a plurality of blind holes (21) in the upper part (2) accommodates a self-tapping screw (23) whose head is spaced closely from one of the faces of the hexagonal nipple head (18). This protects the nipple (16) against rotation, which might cause the passage of the cable (11) through the sealing ring (15) to become non-tight. All the components of the cable lead-in (1) are well protected behind the wall (6) of the casing, while only a relatively low flange (8) on the upper part (2) is present on the outer side of said wall. In practice, this flange cannot be broken off or offer a foothold to a person who might try to stand on the flange.

Description: A cable lead-in The invention concerns a cable lead-in which comprises an upper part and a lower part to be mounted in the mutually assembled state in an opening in a wall of a casing for current conductors, which are connected to an electric cable run through a duct in the upper part. According to present heavy current regulations stripped current conductors in e.g. a terminal block have to be duly shielded against unintentional touch by means of a suitable casing, e.g. a box. When the current conductors are to be connected to other current conductors outside the casing via an electric cable, the cable must therefore be drawn through an opening in the wall of the casing. To prevent the cable from being damaged by the edge of the opening and/or being disconnected from the current conduc¬ tors during this operation, this opening is normally pro¬ vided with a threaded cable joint including a strain re- lief member and usually also a sealing ring as well as a break preventing funnel which is provided on the outermost end part of the threaded joint opposite the current con¬ ductors. The assembled cable entry is thus composed of several co¬ axial components which are arranged successively in the longitudinal direction. The cable entry is therefore rela¬ tively long, and since it is moreover fixed freely canti- levered in the wall of the casing, it is very liable to be broken off completely or partly. This applies especially to cable entries to mobile machinery, such as e.g. indu¬ strial vacuum cleaners, welding units and measuring tables, which are often relatively low with low cable entries which will easily abut obstacles when the machine in question is moved, just as the cable entry may be broken if a person steps on it. If the cable entry is broken, the cable relief member is usually rendered inoperative, involving the risk of the cable being torn loose from its connection to the current conductors such that the power supply to the machine is interrupted. Since the stripped conductor ends of the cable are now exposed, this may moreover result in short- circuiting and current leakage to machine parts which will thereby become conductive. The latter situation is ex¬ tremely dangerous, since a person touching the conducting parts may be injured and in some cases even so seriously that it may proove fatal. Accordingly, there is a need for an improved cable lead-in of the type mentioned in the opening paragraph, which, when mounted on even mobile machinery, cannot in practice be broken by arbitrary impacts, or because a person steps on it. The novel and unique features of the invention achieving this object are that at any rate an outermost section of the duct of the cable lead-in is constructed as a funnel converging inwardly in a direction toward the current con- ductors, and that the upper part is moreover provided with a flange which has a smaller heigth than the axial extent of the funnel and is intended to engage the outer side of a rim around the wall opening in the mounted state. In contrast to the conventional structures, the major part of the cable lead-in is now protected behind the casing, while it is just the actual flange which is present on the outer side of the casing. However, the flange per se is so low that it cannot be broken off by arbitrary impacts, nor does it present sufficient space for a person to get a foothold. When the cable is subjected to a lateral pull, the in¬ wardly converging funnel of the upper part protects the cable against being bent or deflected more than it can stand. Further, to satisfy the additional requirements which must usually be made with respect to a cable lead-in of this type, the cable lead-in may advantageously be equipped with a threaded cable joint, which usually com¬ prises both a cable relief member and a sealing ring to ensure that the cable is sealingly run through. However, according to the invention the threaded cable joint is now arranged in axial extension of the upper part end which is positioned behind the casing, which thus serves to protect all the vulnerable parts of the assembled structure against being damaged. In a particularly simple and advantageous embodiment of the invention the threaded cable joint may comprise an interiorly threaded innermost section of the duct of the upper part and a nipple to be screwed into these threads, and a seat for the sealing ring may be provided between this threaded section and the funnel-shaped section of the duct, said nipple being adapted to press the sealing ring tightly against the seat as well as the cable when being clamped. Further advantageous embodiments as well as advantages achieved by means of the invention will be explained more fully below with reference to the drawing, which shows a structure by way of example, and in which Fig. 1 is a cross-section through a cable lead-in accord¬ ing to the invention with mounted threaded cable joint, fig. 2 is a partially sectional view of the upper part of the cable lead-in shown in fig. 1, and fig. 3 is an end view of the same. Fig. 1 shows a typical cable lead-in according to the in¬ vention. The cable lead-in, which is generally designated by the reference numeral 1, comprises an upper part 2 and a lower part 3. The upper part 2 has a cylindrical member 4 with external threads 5. The cylindrical member 4 is passed through the opening 7 in a wall 6 of a casing to protect some current conductors (not shown) in e.g. a ter- minal block. In the mounted state the upper part 2 engages the outer side of the wall 6 with a flange 8. In the shown case the lower part 3 is in the form of a nut and serves to clamp the upper part 2 fixedly in the opening 7 of the casing wall 6. The upper part 2 is formed with a through duct 10 through which a cable 11 is run; the cable has been or is to be connected to the current conductors (not shown) behind the wall 6 of the casing. This duct 10 has an outermost, funnel-shaped section 12 to ensure that when pulled late¬ rally the cable is bent softly and gently without being damaged. The duct 10 moreover has an innermost threaded section 13, and a seat 14 for an elastomeric sealing ring 15, which may e.g. be of rubber, is formed between these two sections 12, 13. A nipple 16, which has been threaded into the threaded section 13 of the duct 10, presses with its end face via a ring disc 17 against the elastomeric sealing ring 15 which is thereby deformed so as to seal¬ ingly engage both the seat 14 and the cable 11. This en- sures that the cable is run through sealingly. The nipple 16 has a head 18 which may e.g. be hexagonal such that the nipple can be clamped by means of a key. This head is formed with a strain relief member which, in the shown case, is described in the applicant's Danish patent No. 161996, and which comprises a transverse duct 19 provided in the nipple head 18 and a strain relief strap 20 run in parallel in said transverse duct. As will be seen from figs. 2 and 3, a plurality of blind holes 21, which terminate in the innermost end 22 of the upper part 2, are provided in a circle around the duct 10. These blind holes form recesses in the upper part 2, which may e.g. be moulded of plastics. The presence of the blind holes is advantageous when the upper part is to be moulded, and serves in this connection to neutralize ten¬ sions that might occur during cooling. One of the blind holes 21 accommodates a self-tapping screw 33 having a head 24 which is spaced closely from one of the hexagonal faces of the nipple head 18. This prevents a cable, which has been fixed in the nipple by means of a strain relief strap, from rotating the nipple such that the sealing ring 15 no longer sealingly engages the cable 11 if this is twisted. As will be seen, the cable lead-in of the invention satis¬ fies all the requirements which must be made with respect to a conventional cable lead-in of this type. Thus, the cable lead-in has a break prevention funnel protecting the cable against damage when being bent, as well as a sealing ring to ensure sealing run-through of the cable and a strain relief member to protect the cable against being torn loose from its connection to the current conductors which are protected behind the wall of the casing. In the cable lead-in of the invention all vulnerable components are also protected behind this wall, while only the flange 8 is present on the outer side of the wall. However, the height of the flange 8 is so low that in practice the flange cannot be broken off or offer a foothold to a per¬ son who might try to stand on it. For the flange to have a sufficient strength while being too low to offer a foothold, the ratio of the axial extent of the funnel to the heigth of the flange may advantage¬ ously be in the range between 2-7, preferably between 3-6 and in particular between 4-5. In a particularly advan¬ tageous embodiment the height of the flange is moreover less than 10 mm. Although the joint between the upper part 2 and the lower part 3 has been described above and shown in the drawing as a threaded joint, it may be of any other suitable type. For example, the lower part 3 may be in the form of a split ring disc which is passed into a groove in the upper part, and the upper part per se may be provided with a snap lock mechanism having barbs to grip directly behind the rear side of the wall 6. If the wall 6 moverover has a sufficient thickness, its opening 7 may be provided with interior threads for the screwing-in of the upper part.

Claims: P a t e n t C l a i m s 1. A cable lead-in comprising an upper part and a lower part to be mounted mutually assembled in an opening in a wall of a casing for current conductors, which' are con¬ nected to an electric cable run through a duct in the upper part, c h a r a c t e r i z e d in that at any rate an outermost section of this duct is formed as a funnel converging inwardly in a direction toward the current con¬ ductors, and that the upper part is moreover provided with a flange which has a smaller heigth than the axial extent of the funnel and is intended to engage the outer side of a rim around the wall opening in the mounted state. 2. A cable lead-in according to claim 1, c h a r a c ¬ t e r i z e d in that it comprises a threaded cable joint which is arranged on the innermost side of the upper part facing the current conductors. 3. A cable lead-in according to claim 2, c h a r a c ¬ t e r i z e d in that the threaded cable joint comprises an interiorly threaded innermost section of the duct of the upper part and a nipple to be screwed into said threads. 4. A cable lead-in according to claim 2 or 3, wherein the threaded cable joint moreover comprises a sealing ring for sealing the cable, c h a r a c t e r i z e d in that a seat for the sealing ring is provided between the outer¬ most funnel-shaped section of the duct and its innermost threaded section, and that the nipple is adapted to press the sealing ring sealingly against both the seat and the cable when being clamped. 5. A cable lead-in according to claim 2, 3 or 4, wherein the threaded cable joint comprises a strain relief member, c h a r a c t e r i z e d in that said strain relief member is provided in a nipple section extending freely inwardly from the upper part when the nipple is screwed into it. 6. A cable lead-in according to any of claims 1-5, c h a r a c t e r i z e d in that the ratio of the axial extent of the funnel to the heigth of the flange is in the range between 2-7, preferably between 3-6, and in particu¬ lar between 4-5. 7. A cable lead-in according to any of claims 1-6, c h a r a c t e r i z e d in that the heigth of the flange is less than 10 mm. 8. A cable lead-in according to any of claims 1-7, c h a r a c t e r i z e d in that the joint between the upper part and the lower part is a threaded joint. 9. A cable lead-in according to any of claims 1-8, c h a r a c t e r i z e d in that a plurality of blind holes, which terminate in the end face of the upper part facing toward the current conductors, are provided in the upper part in a circle around its duct. 10. A cable lead-in according to claim 9, c h a r a c ¬ t e r i z e d in that at least one face, preferably ex- tending in parallel with the axis of the nipple, is pro¬ vided exteriorly on a nipple section which extends freely inwardly from the upper part when the nipple is screwed into it, and that at any rate one of the blind holes ac¬ commodates a protruding screw, pin or similar member, said screw or pin being arranged at such a radial distance from the axis of the nipple that said at least one face abuts the screw upon rotation.

Inventors: JOHANNSEN OLAF, JOHANNSEN, OLAF
Applicants: JOHANNSEN OLAF, JOHANNSEN OLAF APS, JOHANNSEN, OLAF, OLAF JOHANNSEN APS
Application year: 1994
Main classification: H02G3
IPC codes: H02G3